Various functionalities within a controller for internal combustion engines, such as diagnoses or adaptations, require defined operating states of the internal combustion engine, such as idling, or specific load/rotational speed profiles, in order to be able to run. If such operating states do not occur during a driving cycle, the functions are also unable to run.
A method for operating a vehicle drive and a device for implementing the method are described in German Patent Application No. DE 10 2004 0445 507, filed on Sep. 15, 2004. A method for operating a vehicle drive is described, the vehicle drive having at least one internal combustion engine and at least one electric machine mechanically coupled to the at least one internal combustion engine as well as an energy accumulator actively connected to the electric machine and/or the internal combustion engine. The at least one internal combustion engine and the at least one electric machine generate a requested setpoint drive torque Msetpoint generally jointly. A requested optimal setpoint torque Mv, MVM setpoint opt of the internal combustion engine is limited to an optimized minimum torque MVM min opt above a minimum torque MVM min of the internal combustion engine and/or an optimized maximum torque MVM max opt below a maximum torque MVM max of the internal combustion engine. A rate of change of optimal setpoint torque MVM opt of the internal combustion engine is limited.
In vehicles having a hybrid drive, one objective is to operate the internal combustion engine in the range of favorable efficiencies, to switch the internal combustion engine off when the vehicle is at a standstill or at low vehicle speeds and drive it electrically as well as to utilize braking energy through recuperation. In parallel hybrids, the torques of the internal combustion engine and the torques of one or a plurality of electric drives are added to a drive train torque. The electric drives may be connected, for example as starter generators to the belt drive or the crankshaft of the internal combustion engine. In modern internal combustion engines, various operating points may be problematic with regard to exhaust emissions and fuel consumption. In spark-ignited internal combustion engines, high torques may, for example require a departure from the stoichiometric air-fuel mixture; a full-power mixture enrichment may also be necessary to keep component temperatures within allowed limits. In order to set very low torques, it is customary to displace the ignition angle on the internal combustion engine in the retarded direction, which is also used to achieve derivative-action torque, in order, for example, to build up torque faster from idling. However, the ignition angle displacement brings reduced efficiency. In connection with overrun fuel cutoffs, increased nitrogen oxide emissions may arise due to surplus oxygen in the catalytic converter. Also, the operation of self-igniting internal combustion engines at high torques is expected to result in increased blackening rates and nitrogen oxide emissions; in contrast, operation of self-igniting internal combustion engines at low torques brings the risk that the catalytic converter will cool down.